In recent years, from the perspective of public health and food safety, there has been an increasing need for inspection for foreign matter that may be contained inside food products.
While the methods of X-ray inspection are numerous, an inspection method that is receiving attention is a method in which X-rays are used to collect information on a substance inside a food product. As an example for achieving the foregoing, a so-called in-line-type X-ray inspection apparatus is known. In the in-line-type X-ray inspection apparatus, an X-ray tube and a detector are arranged above and below a conveyor belt that is sandwiched therebetween. The in-line-type X-ray inspection apparatus uses X-rays to inspect a food product to be inspected that is placed on the belt. In this apparatus, the food product to be inspected is placed on the belt (line) and conveyed such as to pass through an X-ray radiation field of the X-ray tube. The scan direction of X-rays is made to agree with the belt conveyance direction.
In this way, food passes through a space between the X-ray tube and the detector (i.e., an object space), and the X-rays which have been transmitted through the food are detected by the detector located under the belt. The detected data is then used to generate images by a processor such as a computer. The generated images are then subjected to an image process conducted by software, for instance, thereby examining existence/non-existence or types of foreign matter which may contaminate the food. The object being examined is not always limited to food, but may be any item which causes significant contrast differences by the X-rays. Such objects may be an object whose size, shape and/or weight should be necessary to be measured accurately.
As a detector which can be mounted in an X-ray inspection apparatus, there is known an X-ray detector disclosed by Patent Reference 1. This X-ray detector is provided as a radiation detector equipped with a plurality of modules each having a plurality of detection elements each composing a pixel, The respective pixels convert incident X-rays to electrical data whose amounts correspond to the X-ray amounts. In this detector, there is provided a scan direction which is set to agree with one of the first X-axis and the first Y-axis perpendicular to the first X-axis. The plural modules are aligned juxtaposed to each other, but with a known gap width formed therebetween, along at least one of the first X- and Y-axes on the same plane. The plural detection elements of the modules are located obliquely to the first X-axis (or the first Y-axis) and two-dimensionally allocated along the second X- and Y-axes perpendicular to each other.
Moreover, the X-ray detector disclosed by this Patent Reference 1 is intended to perform correction for a reduction of X-ray amounts and influence resulting from non-existent pixels between mutually adjacent modules, that is, GAP correction. For this purpose, the plural modules are arranged obliquely to the scan direction, whereby the pixels of each of the modules are also allocated obliquely to the scan direction. It is therefore possible to virtually assign pixel values to the gaps when being scanned, thus greatly reducing influence of the non-sensitive zones of the detector on images to be generated.